1. Field of Invention
The present invention relates to zoom lens devices, optical apparatuses using zoom lens devices, and projectors using zoom lens devices. More specifically, the present invention relates to a structure of a zoom lens device.
2. Description of Related Art
In apparatuses, such as projectors, single lens reflex cameras, video cameras, electronic cameras, medical equipment, and the like, zoom lens devices are used for performing zooming from wide angle to telephoto, or from telephoto to wide angle. In zoom lens devices, a plurality of lens groups, each group including one or more lenses, are arranged along the optical axis. The lens groups can include a focusing lens group and a variator lens group, which is used for changing magnification. The focusing lens group can include two lens groups, which move along the optical axis during the zooming operation. In addition, in zoom lens devices, the focal point changes as the variator lens group moves during the zooming operation. Thus, in order to compensate for the change in focal point, a compensator lens group, which moves in association with the variator lens group along the optical axis, is disposed between the two lens groups forming the variator lens group.
In a zoom lens device which is constructed as described above, the focusing lens group, the variator lens group, and the compensator lens group move along the optical axis during the zooming operation. Accordingly, the zoom lens device may be constructed such that the lens groups are retained by a common lens frame and are moved together. However, although described above as moving in association with the variator lens group, the compensator lens group should move in a different manner. Accordingly, when the focusing lens group, the variator lens group, and the compensator lens group are retained and moved together, appropriate compensation cannot be performed.
Therefore, in the known art, the moveable lens groups, such as the focusing lens group, the variator lens group, and the compensator lens group, which move along the optical axis during the zooming operation, are each retained by a lens frame and are driven individually. More specifically, although the two lens groups forming the variator lens group are moved in the same direction, they are retained by different lens frames and are driven individually.
In order to drive the lens groups, each of the lens frames retaining the moveable lens groups are provided with driving pins which project therefrom, and the driving pins are fitted inside cam grooves formed in a common zoom ring. Since the movement of each moveable lens groups along the optical axis during the zooming operation is determined by the cam grooves, each of the cam grooves is formed in a predetermined pattern corresponding to the movement of each of the moveable lens groups.
In the zoom lens devices of the known art, although decentering, that is, displacement between optical axes, in an individual lens group can be relatively easily corrected, the decentering between the lens groups cannot be corrected. Accordingly, there is a problem in that degradation of optical characteristics, for example, aberration and flare caused by aberration, due to decentering between the lens groups cannot be removed. In addition, when a fault, such as aberration and flare caused by the aberration, occurs due to the decentering between the lens groups, it requires extremely complex operations to determine which one of the lens groups has the problem. Thus, it is impossible to perform such operations in a mass production process.